Vehicle

ABSTRACT

A vehicle includes a friction clutch located between an engine and a driving wheel; a clutch actuator arranged to disengage and engage the friction clutch; a clutch actuator control section arranged and programmed to control the clutch actuator; a slip detection section arranged to detect a slip of the driving wheel; and an engine control section arranged and programmed to decrease an output of the engine when the slip of the driving wheel is detected by the slip detection section. When the friction clutch is in a half clutch state and the slip of the driving wheel is detected, the clutch actuator control section is arranged and programmed to control the clutch actuator so as to maintain a pushing force of the friction clutch at a fixed or substantially fixed level.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a vehicle including a traction controldevice that prevents slippage of a driving wheel.

The present application claims priority from Japanese Patent ApplicationNo. 2012-178449, filed on Aug. 10, 2012, which is incorporated byreference herein in its entirety.

2. Description of the Related Art

Conventionally, as described in, for example, JP H07-103009, a vehicleincluding a traction control device is known. When a driving wheel slipsat the time of starting or changing a gear of the vehicle, the tractioncontrol device decreases an output of an engine to suppress the slip.

Also conventionally, a vehicle including an automatic clutch which isautomatically engaged or disengaged without being operated by a rider isknown. Known automatic clutches include, for example, a clutch which isengaged or disengaged by an actuator such as an electric motor or thelike.

FIG. 7 is an example of a timing diagram obtained in the case where avehicle including a traction control device described in JP H07-103009also includes an automatic clutch and is subjected to traction control.In this example, the clutch is engaged or disengaged in accordance withthe rotation speed (number of rotations per unit time; see referencecharacter c2 in FIG. 7) of the engine. Therefore, at the time ofstarting or changing a gear of the vehicle, the clutch is put into ahalf clutch state from a disengaged state in accordance with an increaseof the rotation speed of the engine (see arrow X1 in FIG. 7). When, atthis point, the driving wheel slips with respect to a road surface (seearrows X2 in FIG. 7), the traction control device performs control todecrease the output of the engine in order to suppress the slip (seearrow X3 in FIG. 7). As a result, the rotation speed of the engine isdecreased (see arrow X4 in FIG. 7), and therefore the clutch is shiftedtoward a position at which the clutch is disengaged (hereinafterreferred to as a “disengagement position”; see arrow X5 in FIG. 7). As aresult of the clutch being shifted toward the disengagement position, atorque conveyed from the engine to the driving wheel is decreased.Therefore, the amount of slip of the driving wheel (see referencecharacter d3 in FIG. 7) is decreased (see arrow X6 in FIG. 7). When theamount of slip of the driving wheel is decreased, the traction controldevice increases the output of the engine (see arrow X7 in FIG. 7) andincreases the rotation speed of the engine (see arrow X8 in FIG. 7).When, at this point, the clutch is shifted toward a position at whichthe clutch is engaged (hereinafter, referred to as an “engagementposition”; see arrow X9 in FIG. 7) as a result of the increase of theoutput of the engine, the torque conveyed to the driving wheel isincreased. Therefore, the driving wheel may slip again. As a result ofthe above-described series of operations being repeated, vibration isgenerated based on hunting of the clutch position, and thus the comfortof riding is lowered. In FIG. 7, reference character a1 represents anaccelerator opening, reference character c1 represents a rotation speedof a main shaft, and reference character c3 represents a differencebetween the rotation speed of the engine and the rotation speed of themain shaft. Reference character d1 represents the rotation speed of thedriving wheel, and reference character d2 represents a rotation speed ofa subordinate wheel.

SUMMARY OF THE INVENTION

Preferred embodiments of the present invention provide a vehiclearranged to suppress a slip of a driving wheel at the time of startingor changing a gear of the vehicle and to also suppress the generation ofvibration based on hunting of the clutch position to improve the comfortof riding.

A vehicle according to a preferred embodiment of the present inventionincludes an engine; a driving wheel drivable by the engine; a frictionclutch located between the engine and the driving wheel; a clutchactuator arranged to disengage and engage the friction clutch; a clutchstate detection device arranged to detect a half clutch state of thefriction clutch; a driving wheel detection sensor arranged to detect arotation speed of the driving wheel; a vehicle speed detection sensorarranged to detect a vehicle speed; a traction control device includinga slip detection section arranged to detect a slip of the driving wheelbased on the rotation speed of the driving wheel detected by the drivingwheel detection sensor and the vehicle speed detected by the vehiclespeed detection sensor, and an engine control section arranged andprogrammed to perform control to decrease an output of the engine whenthe slip of the driving wheel is detected by the slip detection section;and a clutch actuator control device arranged and programmed to controlthe clutch actuator based on a rotation speed of the engine. When thefriction clutch is in a half clutch state and the slip of the drivingwheel is detected, the clutch actuator control device controls theclutch actuator so as to keep a pushing force of the friction clutch ata fixed level.

When the friction clutch is in a half clutch state and the driving wheelslips, the engine control section of the traction control deviceperforms the control to decrease the output of the engine, and thereforecan suppress and prevent an increase of the amount of slip of thedriving wheel. When the friction clutch is in a half clutch state andthe slip of the driving wheel is detected, the clutch actuator controldevice is arranged and programmed to control the clutch actuator so asto keep the pushing force of the friction clutch at a fixed level. As aresult, even if the output and the rotation speed of the engine continuedecreasing, the friction clutch is kept at a fixed position. Therefore,the friction clutch can be engaged swiftly. As a result, the decrease ofthe output of the engine can be conveyed to the driving wheel quickly,and thus the amount of slip can be decreased swiftly. In this manner,when the friction clutch is in a half clutch state and the driving wheelslips, the clutch actuator is controlled so as to keep the pushing forceof the friction clutch at a fixed level. Therefore, the position of thefriction clutch is not changed, and vibration based on the hunting ofthe clutch position is not generated. In addition, since the frictionclutch can be engaged swiftly, the amount of slip can be decreasedswiftly. When the friction clutch is in a half clutch state, it isconceivable to prohibit the engine control section of the tractioncontrol device from performing the control to decrease the output of theengine. In this case, the control to decrease the output of the engineis not performed until the friction clutch is engaged. Therefore, thehunting of the clutch position does not occur, and thus no vibration isgenerated. However, the control to decrease the output of the engine isnot performed when the friction clutch is in a half clutch state.Therefore, a slip of the driving wheel, if occurring when the frictionclutch is in a half clutch state, cannot be suppressed. Such a slip ofthe driving wheel lowers the comfort of riding. Accordingly, the effectsprovided by the vehicle according to a preferred embodiment of thepresent invention are not provided by prohibiting the control todecrease the output of the engine when the friction clutch is in a halfclutch state.

According to a preferred embodiment of the present invention, when thefriction clutch is in a half clutch state and the slip of the drivingwheel is detected, the clutch actuator control device is arranged andprogrammed to control the clutch actuator so as to keep the pushingforce of the friction clutch at a level thereof at the time when theslip is detected.

As a result, the friction clutch can be engaged swiftly by the outputand the rotation speed of the engine is continued to be decreased. As aresult, the decrease of the output of the engine can be conveyed to thedriving wheel quickly, and thus the amount of slip can be decreasedswiftly.

According to a preferred embodiment of the present invention, thevehicle further includes a hydraulic cylinder arranged to generate anoil pressure by driving the clutch actuator. When the friction clutch isin a half clutch state and the slip of the driving wheel is detected,the clutch actuator control device controls the clutch actuator so as tokeep the oil pressure of the hydraulic cylinder at a fixed level andthus keeps the pushing force of the friction clutch at a fixed level.

In this manner, the oil pressure of the hydraulic cylinder is kept at afixed level, and thus the pushing force of the friction clutch can bekept at a fixed level.

According to a preferred embodiment of the present invention, when thefriction clutch is in a half clutch state and the slip of the drivingwheel is detected, the clutch actuator control device is arranged andprogrammed to control the clutch actuator so as to keep a position ofthe friction clutch at a fixed position.

As a result, the friction clutch can be engaged swiftly by the outputand the rotation speed of the engine being kept decreasing. As a result,the decrease of the output of the engine can be conveyed to the drivingwheel quickly, and thus the amount of slip can be swiftly decreased.

According to a preferred embodiment of the present invention, when thefriction clutch is in a half clutch state and the slip of the drivingwheel is detected, the clutch actuator control device controls theclutch actuator so as to keep a position of the friction clutch at aposition thereof at the time when the slip is detected.

As a result, the friction clutch can be engaged swiftly by the outputand the rotation speed of the engine being kept decreasing. As a result,the decrease of the output of the engine can be conveyed to the drivingwheel quickly, and thus the amount of slip can be swiftly decreased.

According to a preferred embodiment of the present invention, thefriction clutch includes a driving-side rotation body to which a torqueof the engine is conveyed and a subordinate-side rotation body capableof contacting, and being separated from, the driving-side rotation body;the vehicle further includes a clutch rotation speed differencedetection device arranged to detect a rotation speed difference betweenthe driving-side rotation body and the subordinate-side rotation body ofthe friction clutch; and when the rotation speed difference between thedriving-side rotation body and the subordinate-side rotation body of thefriction clutch becomes substantially zero while the clutch actuatorcontrol device controls the clutch actuator so as to keep the pushingforce of the friction clutch at a fixed level, the clutch actuatorcontrol device stops controlling the clutch actuator so as to keep thepushing force of the friction clutch at a fixed level and controls theclutch actuator so as to engage the friction clutch.

As a result, when the rotation speed of the driving-side rotation bodyand the rotation speed of the subordinate-side rotation body of thefriction clutch become substantially equal to each other, the control tokeep the pushing force of the friction clutch at a fixed level isstopped and the control to engage the friction clutch is performedpromptly. Thus, the decrease of the output of the engine can be conveyedto the driving wheel quickly. As a result, the amount of slip can beswiftly decreased.

According to a preferred embodiment of the present invention, thevehicle further includes an engine rotation speed sensor arranged todetect the rotation speed of the engine. When the rotation speed of theengine becomes equal to or lower than a prescribed value while theclutch actuator control device controls the clutch actuator so as tokeep the pushing force of the friction clutch at a fixed level, theclutch actuator control device stops controlling the clutch actuator soas to keep the pushing force of the friction clutch at a fixed level andcontrols the clutch actuator so as to disengage the friction clutch.

In this manner, when the rotation speed of the engine becomes equal toor lower than a prescribed value, the control to keep the pushing forceof the friction clutch at a fixed level is stopped and the control todisengage the friction clutch is performed. Thus, engine stall can beprevented.

According to a preferred embodiment of the present invention, when thefriction clutch is in a half clutch state and the slip of the drivingwheel is not detected, the clutch actuator control device is arrangedand programmed to control the clutch actuator so as to engage thefriction clutch when the rotation speed of the engine is increased andcontrols the clutch actuator so as to disengage the friction clutch whenthe rotation speed of the engine is decreased.

As a result, the friction clutch can be engaged and disengaged easily.

According to a preferred embodiment of the present invention, thevehicle further includes a stepped transmission mechanism and a shiftactuator arranged to drive the transmission mechanism.

Since the change of the gear position of the transmission mechanism canbe performed by use of the shift actuator, the operability for the rideris improved. If hunting of the clutch position occurs when thetransmission mechanism is controlled by the shift actuator, this mayadversely influence the change of the gear position of the transmissionmechanism. However, according to a preferred embodiment of the presentinvention, the hunting of the clutch position does not occur. Therefore,even when the transmission mechanism is controlled by the shiftactuator, there is no adverse influence on the change of the gearposition of the transmission mechanism.

According to a preferred embodiment of the present invention, thevehicle further includes a shift actuator control device arranged andcontrolled to drive the transmission mechanism by use of the shiftactuator after the friction clutch starts to be disengaged by the clutchactuator.

As a result, the change of the gear position can be performed in asatisfactory manner.

According to a preferred embodiment of the present invention, thevehicle further includes an electronically controllable throttle valve.When the slip of the driving wheel is detected, the engine controlsection of the traction control device executes control to decrease anopening of the throttle valve.

In this manner, the opening of the throttle valve is decreased, and thusthe output of the engine can be decreased easily.

According to a preferred embodiment of the present invention, thevehicle further includes an ignition device. When the slip of thedriving wheel is detected, the engine control section of the tractioncontrol device executes ignition retarding control on the ignitiondevice.

In this manner, the time of igniting the ignition device is retarded,and thus the output of the engine can be decreased easily.

According to a preferred embodiment of the present invention, thevehicle further includes a fuel injection device. When the slip of thedriving wheel is detected, the engine control section of the tractioncontrol device executes fuel injection amount decreasing control on thefuel injection device.

In this manner, fuel injection from the fuel injection valve is stoppedor the amount of fuel injection is decreased, and thus the output of theengine can be decreased easily.

According to a preferred embodiment of the present invention, thevehicle further includes a subordinate wheel rotating in accordance withrunning of the vehicle; and the vehicle speed detection sensor is asensor arranged to detect a rotation speed of the subordinate wheel.

As a result, the slip detection section can detect the slip of thedriving wheel based on the rotation speed of the subordinate wheeldetected by the vehicle speed detection sensor and the rotation speed ofthe driving wheel detected by the driving wheel detection sensor.

According to a preferred embodiment of the present invention, thevehicle is a motorcycle.

According to a preferred embodiment of the present invention, amotorcycle providing the above-described functions and effects can beprovided.

As described above, the present invention provides a vehicle arranged tosuppress and prevent a slip of a driving wheel at the time of startingor changing a gear of the vehicle and to suppress and prevent thegeneration of vibration based on hunting of the clutch position, andthus improving the comfort of riding.

The above and other elements, features, steps, characteristics andadvantages of the present invention will become more apparent from thefollowing detailed description of the preferred embodiments withreference to the attached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side view of a motorcycle according to a preferredembodiment of the present invention.

FIG. 2 is structural view of an engine according to a preferredembodiment of the present invention.

FIG. 3 is cross-sectional view showing an internal structure of a powerunit according to a preferred embodiment of the present invention.

FIG. 4 is a block diagram showing a portion of the elements of amotorcycle according to a preferred embodiment of the present invention.

FIG. 5 is a flowchart showing control performed at the time of startingof a motorcycle according to a preferred embodiment of the presentinvention.

FIG. 6 is a timing diagram on a clutch pushing force keeping controlperformed on a motorcycle according to a preferred embodiment of thepresent invention.

FIG. 7 is a timing diagram on traction control performed on aconventional vehicle.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, preferred embodiments of the present invention will bedescribed. As shown in FIG. 1, a vehicle according to a preferredembodiment of the present invention is a motorcycle 1. The motorcycle 1is not limited to any specific type and may be of, for example, aso-called scooter type, a moped type, an off-road type, an on-road typeor the like. A vehicle according to the present invention is not limitedto a motorcycle, and may be a saddle type vehicle which a rider (user)rides astride or an equivalent thereof. Saddle type vehicles include,for example, an ATV (All Terrain Vehicle), a four-wheel buggy or thelike in addition to a motorcycle. In FIG. 1, reference characters F andRe respectively represent “front” and “rear”.

As shown in FIG. 1, the motorcycle 1 preferably includes a head pipe 3and a body frame 6. The body frame 6 preferably includes two, i.e., leftand right, frames 6 a extending rearward from the head pipe 3. FIG. 1shows only one frame 6 a. A rear portion of the frame 6 a extendsdownward. The rear portion of the frame 6 a is connected to a rear armbracket 5. The rear arm bracket 5 is connected to a front end portion ofa rear arm 21 via a pivot shaft 22. The rear arm 21 is swingable upwardand downward about the pivot shaft 22. At a rear end portion of the reararm 21, a rear wheel 23 is supported. The rear wheel 23 is a drivingwheel drivable by an engine 45, described later. The motorcycle 1preferably includes a driving wheel detection sensor 92 (see FIG. 4).The driving wheel detection sensor 92 is arranged to detect a rotationspeed of the rear wheel 23. Based on the detected rotation speed, thedriving wheel detection sensor 92 outputs a rear wheel rotation speedsignal to an ECU 100 (Electronic Control Unit), see FIG. 4.

A fuel tank 13 is preferably located above the frame 6 a. A seat 14 onwhich the rider may sit is located rearward of the fuel tank 13.

The head pipe 3 is arranged to support a steering shaft (not shown), anda handle 4 is provided on the steering shaft. The handle 4 is preferablyprovided with a shift switch (not shown). The shift switch preferablyincludes a shift-up switch and a shift-down switch, and can be used toincrease or decrease a transmission gear 49, described later, in therange from a neutral position to a maximum position (e.g., a sixth gear)by a manual operation. The shift switch outputs a gear changeinstruction from the rider to a shift actuator control section 140 (seeFIG. 4) described later.

At a lower portion of the steering shaft, a front fork 10 is provided.At a lower end of the front fork 10, a front wheel 12 is rotatablysupported. The front wheel 12 is a subordinate wheel rotating inaccordance with the running of the motorcycle 1. The motorcycle 1preferably includes a vehicle speed detection sensor 94 (see FIG. 4).The vehicle speed detection sensor 94 is arranged to detect a vehiclespeed of the motorcycle 1. Based on the detected vehicle speed, thevehicle speed detection sensor 94 outputs a vehicle speed signal to theECU 100. The vehicle speed detection sensor 94 may be, for example, asensor arranged to detect a rotation speed of the front wheel 12. Inthis case, the vehicle speed detection sensor 94 outputs a vehicle speedsignal to the ECU 100 based on the detected rotation speed.

A power unit 20 is preferably suspended from the frame 6 a and the reararm bracket 5. FIG. 3 is a cross-sectional view showing an internalstructure of the power unit 20. As shown in FIG. 3, the power unit 20preferably includes at least the engine 45, an automatic clutch 44, anda transmission mechanism 43. The engine 45, the automatic clutch 44, andthe transmission mechanism 43 are preferably integrally assembled with acrankcase 26 (see FIG. 1).

As shown in FIG. 2, the engine 45 includes a cylinder 31, a piston 32reciprocating in the cylinder 31, a crankshaft 25, and a connection rod34 arranged to couple the piston 32 and the crankshaft 25 to each other.The engine 45 preferably includes a fuel injection valve 52, which is afuel injection device arranged to inject fuel, and an ignition device 50arranged to ignite the fuel in a combustion chamber 35. The engine 45preferably includes a crankshaft rotation speed sensor 60 arranged todetect a rotation speed (e.g., a number of rotations per unit time) ofthe crankshaft 25 and a temperature sensor 62 arranged to detect atemperature of the engine 45. Hereinafter, the rotation speed of thecrankshaft 25 will be referred to as the “rotation speed of the engine45”. The fuel injection valve 52 is connected to a fuel tank (notshown). The temperature sensor 62 may detect the temperature of aportion of the engine 45 (e.g., cylinder). In the case where the engine45 is a water-cooled engine, the temperature sensor 62 may alternativelydetect a temperature of the cooling water. Specifically, the temperaturesensor 62 may detect the temperature of the engine 45 directly orindirectly via the cooling water or the like.

The engine 45 preferably includes an intake path 80 arranged tointroduce air to the combustion chamber 35, an intake valve 82 arrangedto open or close the intake path 80 and the combustion chamber 35 withrespect to each other, a discharge path 84 arranged to discharge exhaustgas from the combustion chamber 35, and a discharge valve 86 arranged toopen and close the combustion chamber 35 and the discharge path 84 withrespect to each other. In the present preferred embodiment, the fuelinjection valve 52 is located so as to inject the fuel to the inside ofthe intake path 80. The fuel injection valve 52 may inject the fueldirectly to the inside of the combustion chamber 35. Additionally, theengine 45 may include two types of fuel injection valves arranged toinject the fuel to the inside of the intake path 80 and to the inside ofthe combustion chamber 35, respectively.

In the intake path 80, a pressure sensor 64 is preferably provided todetect an intake pressure, which is an internal pressure of the intakepath 80. In the intake path 80, a throttle valve 54 is located. Thethrottle valve 54 is an electronically controllable valve, a throttleopening of which is controlled by a throttle driving actuator 56. Thethrottle valve 54 adjusts the flow rate or the speed of air flowing inthe intake path 80. A right handle of the motorcycle 1 is provided withan accelerator operator (not shown) for driving arranged to drive thethrottle valve 54 via the throttle driving actuator 56. The acceleratoroperator includes an accelerator opening sensor (not shown) attachedthereto arranged to detect an accelerator opening, which is an operationamount of the accelerator operator, namely, an opening of theaccelerator operator. The throttle valve 54 is preferably provided witha throttle position sensor 66 arranged to detect the opening of thethrottle valve 54. The throttle position sensor 66 outputs a throttleopening signal to the ECU 100.

In the discharge path 84, a catalyst 90 is provided. Also in thedischarge path 84, an O₂ sensor 68 arranged to detect oxygen containedin the exhaust gas is provided as an air-to-fuel ratio sensor. Theair-to-fuel ratio sensor may be any sensor which can detect at leastwhether the air-to-fuel ratio is in a rich region or a lean region. TheO₂ sensor 68 according to the present preferred embodiment can detectwhether the air-to-fuel ratio is in the rich region or the lean region.Needless to say, an element arranged to linearly output an air-to-fuelratio (linear A/F sensor), namely, a sensor arranged to output theair-to-fuel ratio itself may be used as the air-to-fuel ratio sensor.

As shown in FIG. 3, the crankshaft 25 is preferably coupled to a mainshaft 41 via the automatic clutch 44. The main shaft 41 is preferablylocated parallel or substantially parallel to the crankshaft 25. Themain shaft 41 is also preferably located parallel or substantiallyparallel to a drive shaft 42. The main shaft 41 is preferably providedwith a main shaft rotation speed sensor 61 arranged to detect a rotationspeed (number of rotations per unit time) of the main shaft 41.

The automatic clutch 44 according to the present preferred embodimentpreferably includes a multi-plate friction clutch 46 and a clutchactuator 70. The friction clutch 46 is located between the engine 45 andthe rear wheel 23. The friction clutch 46 preferably includes a clutchhousing 443 and a clutch boss 447. Inside the clutch housing 443, aplurality of friction plates 445 are provided as a driving-side rotationbody. A torque of the engine 45 is conveyed to the friction plates 445.Outside the clutch boss 447, a plurality of clutch plates 449 areprovided as a subordinate-side rotation body. Each of the frictionplates 445 rotates together with the clutch housing 443. By contrast,each of the friction plates 445 can be moved in an axial direction ofthe main shaft 41. The plurality of friction plates 445 are locatedalong the axial direction of the main shaft 41. The friction clutch 46may alternatively be a single-plate clutch instead of the multi-plateclutch, if so desired.

Each of the clutch plates 449 faces each of the friction plates 445adjacent thereto. Each of the clutch plates 449 rotates together withthe clutch boss 447. By contrast, each of the clutch plates 449 can bemoved in the axial direction of the main shaft 41. In this preferredembodiment, the plurality of friction plates 445 and the plurality ofclutch plates 449 define a plate group 442.

As shown in FIG. 3, a pressure plate 451 is located outward to the mainshaft 41 in a vehicle width direction (rightward in FIG. 3). Thepressure plate 451 preferably is generally disc-shaped. In an outerportion of the pressure plate 451 in a radial direction thereof, a pressportion 451B protruding toward the plate group 442 is preferablyprovided. The press portion 451B is located at a position facing thefriction plate 445 which is located at the rightmost position in theplate group 442.

The friction clutch 46 is provided with a spring 450. The spring 450urges the pressure plate 451 inward in the vehicle width direction(leftward in FIG. 3). Specifically, the spring 450 urges the pressureplate 451 in a direction in which the press portion 451B presses theplate group 442.

A central portion of the pressure plate 451 is in engagement with an endportion (right end portion in FIG. 3) of a push rod 455 via a bearing457. Thus, the pressure plate 451 is rotatable with respect to the pushrod 455. The main shaft 41 preferably has a tubular shape. The other endportion (left end portion) of the push rod 455 is accommodated in themain shaft 41. In the main shaft 41, a spherical ball 459 is providedadjacent to the other end portion (left end portion) of the push rod455. Also in the main shaft 41, a push rod 461 is provided adjacent tothe ball 459.

A left end portion of the push rod 461 protrudes outward from the mainshaft 41. At the left end portion of the push rod 461, a piston 463 isintegrally provided. The piston 463 is guided by a cylinder main body465 to be slidable in the axial direction of the main shaft 41.

The friction clutch 46 is preferably disengaged or engaged by the clutchactuator 70. The clutch actuator 70 is preferably an electric motor inthe present preferred embodiment, but is not limited thereto. Drivingthe clutch actuator 70 allows the friction plates 445 and the clutchplates 449 to be close to, and thus to be in contact with, each other.Driving the clutch actuator 70 also allows the friction plates 445 andthe clutch plates 449 to be separated from, and thus to be distancedfrom, each other. In this manner, the friction clutch 46 can bedisengaged or engaged.

The clutch actuator 70 is provided with a potentiometer 96 (see FIG. 4).The potentiometer 96 is a clutch actuator sensor arranged to detect adriving amount of the clutch actuator 70. The potentiometer 96 detects arotation angle or a rotation position of the clutch actuator 70. Theclutch actuator 70 and the clutch actuator sensor may be integratedtogether if so desired. An example of such an integrated clutch actuator70 is a servo motor which is arranged to detect a rotation angle and arotation position.

When the clutch actuator 70 is driven, a space 467 enclosed by thepiston 463 and the cylinder main body 465 is supplied with hydraulicoil. A change of the driving force of the clutch actuator 70 adjusts theoil pressure of the hydraulic oil supplied to the space 467 in thecylinder main body 465. When the space 467 is supplied with thehydraulic oil, the piston 463 is pushed and moved rightward in FIG. 3.Thus, the piston 463 pushes the pressure plate 451 rightward in FIG. 3via the push rod 461, the ball 459, the push rod 455 and the bearing457. When the rightward (in FIG. 3) pushing force applied to thepressure plate 451 via the piston 463 is increased, the press portion451B of the pressure plate 451 is separated from the friction plates445. As a result, the friction clutch 46 is put into a disengaged state.In the state where the press portion 451B is separated from the plategroup 442, each friction plate 445 and each clutch plate 449 areseparated from each other, and a small gap is provided between eachfriction plate 445 and each clutch plate 449. Therefore, no frictionforce to convey a torque is generated between each friction plate 445and each clutch plate 449.

For driving the clutch actuator 70 to engage the friction clutch 46, thepushing force applied to the pressure plate 451 via the piston 463 isdecreased and, as a result, the pressure plate 451 is moved leftward inFIG. 3 by the spring 450. When the pressure plate 451 is moved leftwardin FIG. 3, the press portion 451B presses the plate group 442 leftward.As a result, the friction clutch 46 is put into a half clutch state.Specifically, each friction plate 445 and each clutch plate 449 contacteach other and rotate with respect to each other. As a result, thetorque of the engine 45 is conveyed to the main shaft 41 via thefriction plates 445 and the clutch plates 449. As seen from this, the“half clutch state” of the friction clutch 46 refers to a state where aportion of the torque of the engine 45 is conveyed to the main shaft 41via the friction clutch 46 while each friction plate 445 and each clutchplate 449 of the friction clutch 46 rotate with respect to each other.Specifically, the “half clutch state” of the friction clutch 46 refersto a state where the clutch housing 443 (friction plates 445) and theclutch boss 447 (clutch plates 449) are in contact with each other whilethe difference between the rotation speed of the clutch housing 443(friction plates 445) and the rotation speed of the clutch boss 447(clutch plates 449) (the difference will be referred to as the “clutchrotation speed difference of the friction clutch 46”) is not zero.

When the clutch actuator 70 is driven to further decrease the pushingforce applied to the pressure plate 451, the pressure plate 451 is movedfurther leftward in FIG. 3 by the spring 450. As a result, each frictionplate 445 and each clutch plate 449 of the plate group 442 are put intopressure contact with each other. Specifically, the friction clutch 46is put into an engaged state, and each friction plate 445 and eachclutch plate 449 rotate integrally together.

As described above, the pressure plate 451 moves in one direction or theother direction along the axial direction of the main shaft 41 inaccordance with which of the pushing force applied to the pressure plate451 by the driving of the clutch actuator 70 and the urging force of thespring 450 is larger. In accordance with such a movement, the frictionclutch 46 is put into an engaged state, a half clutch state or adisengaged state.

At the crankshaft 25 of the engine 45, a gear 27 is integrallysupported. At the main shaft 41, a gear 441 meshing together with thegear 27 is supported. The gear 441 is rotatable with respect to the mainshaft 41. The gear 441 is preferably provided integrally with, forexample, the clutch housing 443. Thus, the torque of the engine 45 isconveyed from the crankshaft 25 via the gear 441 to the clutch housing443. The torque of the engine 45 is also conveyed from the clutchhousing 443 to the clutch boss 447 by a friction force generated betweenthe plurality of friction plates 445 and the plurality of clutch plates449. The clutch boss 447 and the main shaft 41 integrally rotatetogether. Specifically, the clutch boss 447 and the main shaft 41 do notrotate with respect to each other. Therefore, when the friction clutch46 is engaged, the torque of the engine 45 is conveyed to the main shaft41.

The push rod 455 is not limited to a push rod arranged to push thepressure plate 451 rightward in FIG. 3 by a mechanism inserted throughthe main shaft 41. For example, the push rod 455 may be a push rodarranged to pull the pressure plate 451 rightward in FIG. 3 by amechanism provided outward to the pressure plate 451 in the vehiclewidth direction (rightward in FIG. 3).

The transmission mechanism 43 according to this preferred embodiment ispreferably a so-called dog clutch type and also is a steppedtransmission mechanism. The transmission mechanism 43 is located on apower transmission path arranged to convey the torque of the engine 45to the rear wheel 23 (see FIG. 1) at a position between the frictionplates 445 of the friction clutch 46 and the rear wheel 23. Thetransmission mechanism 43 preferably includes transmission gears 49 and420, a shift cam 421, shift forks 422, a shift actuator 72 and the likedescribed later.

The main shaft 41 preferably includes a plurality of transmission gears49 attached thereto. By contrast, the drive shaft has a plurality oftransmission gears 420 attached thereto corresponding to the pluralityof transmission gears 49. Only a selected transmission gear 49 among theplurality of transmission gears 49 and only a selected transmission gear420 among the plurality of transmission gears 420 are engageable witheach other. At least either the transmission gears 49 among theplurality of transmission gears 49 which are not selected, or thetransmission gears 420 among the plurality of transmission gears 420which are not selected, are rotatable with respect to the main shaft 41or the drive shaft 42. Specifically, at least either the transmissiongears 49 among the plurality of transmission gears 49 which are notselected, or the transmission gears 420 among the plurality oftransmission gears 420 which are not selected, idle with respect to themain shaft 41 or the drive shaft 42. The conveyance of rotation betweenthe main shaft 41 and the drive shaft 42 is performed only via theselected transmission gear 49 and the selected transmission gear 420which are gearing with each other.

The transmission gear 49 and the transmission gear 420 are selected bythe shift cam 421. An outer circumferential surface of the shift cam 421includes a plurality of cam grooves 421 a defined therein. Each shiftfork 422 is attached to each of the cam grooves 421 a. Each shift fork422 is in engagement with a prescribed transmission gear 49 and aprescribed transmission gear 420 for the main shaft 41 and the driveshaft 42. When the shift cam 421 is rotated, the plurality of shiftforks 422 are respectively guided by the cam grooves 421 a to move inthe axial direction of the main shaft 41. In this manner, thetransmission gear 49 and the transmission gear 420 which are to beengaged with each other are selected from the transmission gears 49 andthe transmission gears 420. Specifically, only a pair of transmissiongears, among the plurality of transmission gears 49 and transmissiongears 420, which are at positions corresponding to the rotation angle ofthe shift cam 421 are respectively put into a secured state by a splinewith respect to the main shaft 41 and the drive shaft 42. Thus, a gearposition in the transmission mechanism 43 is determined. As a result,the conveyance of rotation is performed between the main shaft 41 andthe drive shaft 42 at a prescribed gear ratio via the transmission gear49 and the transmission gear 420. The shift cam 421 is rotated by aprescribed angle by a reciprocating movement of a shift rod 75.

Switching of the transmission gears 49 and 420 in the transmissionmechanism 43, namely, the change of the gear position of thetransmission mechanism 43 is performed by driving of the shift actuator72. The shift actuator 72 is preferably an electric motor in the presentpreferred embodiment, but is not limited thereto. The shift actuator 72is connected to the shift cam 421 via the shift rod 75. The shift rod 75is reciprocated by the driving of the shift actuator 72. After thefriction clutch 46 starts to be disengaged by the clutch actuator 70,the shift actuator 72 moves the shift rod 75 and thus switches thetransmission gears of the transmission mechanism 43. The shift actuator72 is provided with a potentiometer (not shown). The potentiometer is ashift actuator sensor arranged to detect a driving amount of the shiftactuator 72. The potentiometer detects a rotation angle or a rotationposition of the shift actuator 72. The shift actuator 72 and the shiftactuator sensor may be integrated together. An example of such anintegrated shift actuator 72 is a servo motor arranged to detect arotation angle and a rotation position.

Owing to the above-described structure, when a prescribed pair oftransmission gears 49 and 420 are respectively secured to the main shaft41 and the drive shaft 42 and the friction clutch 46 is put into a halfclutch state or an engaged state while the engine 45 is driven, thetorque of the engine 45 is conveyed to the main shaft 41 via thefriction clutch 46. The conveyance of rotation is performed between themain shaft 41 and the drive shaft 42 at a prescribed gear ratio via theprescribed pair of transmission gears 49 and 420, and thus the driveshaft 42 is rotated. When the drive shaft 42 is rotated, the torque isconveyed by a power conveyance mechanism 47 (see FIG. 1) arranged toconnect the drive shaft 42 and the rear wheel 23 (see FIG. 1) to eachother, and thus the rear wheel 23 is rotated.

The motorcycle 1 includes the ECU (Electric Control Unit) 100 as acontrol device arranged and programmed to control the engine 45. Asshown in FIG. 4, the ECU 100 preferably includes a clutch statedetection section 105, a slip detection section 110, an engine controlsection 115, a clutch actuator control section 135, and the shiftactuator control section 140.

The clutch state detection section 105 is arranged to detect a halfclutch state of the friction clutch 46 based on the rotation angle orthe rotation position of the clutch actuator 70 which is detected by thepotentiometer 96. For example, when the rotation angle of the clutchactuator 70 is equal to or smaller than a prescribed rotation angle θ1,the friction clutch 46 is detected as being in an engaged state. Whenthe rotation angle of the clutch actuator 70 is equal to or larger thana prescribed rotation angle θ2, the friction clutch 46 is detected asbeing in a disengaged state. When the rotation angle of the clutchactuator 70 is larger than θ1 and smaller than θ2, the friction clutch46 is detected as being in a half clutch state. In the case where aservo motor arranged to detect the rotation angle and the rotationposition is used as the clutch actuator 70, the clutch state detectionsection 105 can detect the state of the friction clutch 46 based on therotation angle or the rotation position detected by the servo motor.

The slip detection section 110 is arranged to detect a slip of the rearwheel 23 based on the rotation speed of the rear wheel 23 detected bythe driving wheel detection sensor 92 and the vehicle speed detected bythe vehicle speed detection sensor 94. The slip detection section 110 isarranged to detect a slip of the rear wheel 23 also based on therotation speed of the rear wheel 23 detected by the driving wheeldetection sensor 92 and the rotation speed of the front wheel 12detected by the vehicle speed detection sensor 94. The slip detectionsection 110 detects the slip of the rear wheel 23 when, for example, thedifference between the rotation speed of the rear wheel 23 and therotation speed of the front wheel 12 is larger than a preset value.

The engine control section 115 is arranged and programmed to adjust theoutput of the engine 45. The engine control section 115 preferablyincludes an ignition control section 120, an injection control section125, and a throttle valve control section 130. The ignition controlsection 120 is arranged and programmed to control the ignition device50, for example, by giving a pulse signal to the ignition device 50. Theinjection control section 125 is arranged and programmed to control thefuel injection valve 52, for example, by giving a pulse signal to thefuel injection valve 52. The throttle valve control section 130 isarranged and programmed to control the opening of the throttle valve 54,for example, by driving the throttle driving actuator 56 based oninformation from the accelerator opening sensor. The engine controlsection 115 is arranged and programmed to adjust the output of theengine 45 by controlling the ignition device 50, the fuel injectionvalve 52, and the opening of the throttle valve 54.

When the friction clutch 46 is in an engaged state or a half clutchstate and the slip detection section 110 has detected a slip of the rearwheel 23, the engine control section 115 is arranged and programmed toperform control to decrease the output of the engine 45 (hereinafter,referred to also as “traction control”). The traction control may be,for example, control to retard the time of igniting the ignition device50 (hereinafter, referred to as “ignition retarding control”), controlto stop fuel injection or decrease the amount of fuel injection from thefuel injection valve 52 (hereinafter, referred to as “fuel injectionamount decreasing control”), control to decrease the opening of thethrottle valve 54, or a combination thereof.

The clutch actuator control section 135 is arranged and programmed tocontrol the clutch actuator 70. The clutch actuator 70 can be drivenbased on, for example, the control of the clutch actuator controlsection 135. The clutch actuator control section 135 controls the clutchactuator 70 based on the rotation speed of the engine 45. When, forexample, the friction clutch 46 is in a half clutch state and a slip ofthe rear wheel 23 is not detected, the clutch actuator control section135 controls the clutch actuator 70 so as to engage the friction clutch46 when the rotation speed of the engine 45 is increased, and controlsthe clutch actuator 70 so as to disengage the friction clutch 46 whenthe rotation speed of the engine 45 is decreased.

When the friction clutch 46 is in a half clutch state and a slip of therear wheel 23 is detected, the clutch actuator control section 135 isarranged and programmed to control the clutch actuator 70 so as to keepthe pushing force of the friction clutch 46 at a fixed level(hereinafter, referred to also as “clutch pushing force keepingcontrol”). The pushing force of the friction clutch 46 is a pushingforce applied to the pressure plate 451 by the driving of the clutchactuator 70. The pushing force of the friction clutch 46 can bedetermined, for example, based on the driving force of the clutchactuator 70 or the oil pressure of the hydraulic oil supplied to thespace 467 of the cylinder main body 465. The clutch actuator controlsection 135 keeps the pushing force of the friction clutch 46 at a fixedlevel, and thus can keep the position of the friction clutch 46 at afixed position. When the friction clutch 46 is in a half clutch stateand a slip of the rear wheel 23 is detected, the clutch actuator controlsection 135 is arranged and programmed to control the clutch actuator 70so as to keep the position of the friction clutch 46 at a fixedposition. The clutch actuator control section 135 also keeps the oilpressure of the hydraulic oil supplied to the space 467 of the cylindermain body 465 at a fixed level, and thus can keep the pushing force ofthe friction clutch 46 at a fixed level. When the friction clutch 46 isin a half clutch state and a slip of the rear wheel 23 is detected, theclutch actuator control section 135 controls the clutch actuator 70 soas to keep the oil pressure of the hydraulic oil supplied to the space467 of the cylinder main body 465 at a fixed level, and thus can keepthe pushing force of the friction clutch 46 at a fixed level.

The position of the friction clutch 46 can preferably be indirectlydetermined based on the rotation angle or the rotation position detectedby the potentiometer 96 provided to the clutch actuator 70. The positionof the friction clutch 46 can also be determined, for example, byproviding a clutch position detection sensor arranged to detect theposition of the friction clutch 46. For example, the clutch positiondetection sensor can be provided to the pressure plate 451 to directlydetect the position of the pressure plate 451, so that the position ofthe friction clutch 46 is detected. The expression “keep the position ofthe friction clutch 46 at a fixed position” refers to a state where thepushing force applied to the pressure plate 451 by the driving of theclutch actuator 70 and the urging force of the spring 450 are equal toeach other and thus the pressure plate 451 of the friction clutch 46 isnot moved from a prescribed position.

Preferably, when the friction clutch 46 is in a half clutch state and aslip of the rear wheel 23 is detected, the clutch actuator controlsection 135 is arranged and programmed to control the clutch actuator 70so as to keep the pushing force of the friction clutch 46 at a levelthereof at the time when the slip of the rear wheel 23 is detected. Thepushing force of the friction clutch 46 may be a pushing force that ispredefined regardless of the pushing force of the friction clutch 46 atthe time when the slip of the rear wheel 23 is detected. When thefriction clutch 46 is in a half clutch state and a slip of the rearwheel 23 is detected, the clutch actuator control section 135 can alsocontrol the clutch actuator 70 so as to keep the position of thefriction clutch 46 at a position thereof at the time when the slip ofthe rear wheel 23 is detected. The position at which the friction clutch46 is kept may be, for example, a position thereof when a prescribedtime duration passes after the slip of the rear wheel 23 is detectedwhile the friction clutch 46 is in a half clutch state.

When the clutch rotation speed difference of the friction clutch 46becomes substantially zero, the clutch actuator control section 135 isarranged and programmed to engage the friction clutch 46. The clutchrotation speed difference of the friction clutch 46 is the rotationspeed difference between the clutch housing 443 (friction plates 445)and the clutch boss 447 (clutch plates 449), and is the same as thedifference between the rotation speed of the engine 45 (rotation speedof the crankshaft 25) and the rotation speed of the main shaft 41. Theclutch rotation speed difference can be calculated by use of therotation speed of the crankshaft 25 detected by the crankshaft rotationspeed sensor 60 and the rotation speed of the main shaft 41 detected bythe main shaft rotation speed sensor 61.

When the clutch rotation speed difference of the friction clutch 46becomes substantially zero while the clutch actuator control section 135controls the clutch actuator 70 so as to keep the pushing force of thefriction clutch 46 at a fixed level, the clutch actuator control section135 stops controlling the clutch actuator 70 so as to keep the pushingforce of the friction clutch 46 at a fixed level and controls the clutchactuator 70 so as to engage the friction clutch 46. The clutch actuatorcontrol section 135 operates in substantially the same manner whilecontrolling the clutch actuator 70 so as to keep the position of thefriction clutch 46 at a fixed position.

When the rotation speed of the engine 45 becomes equal to or lower thana prescribed rotation speed, the clutch actuator control section 135 isarranged and programmed to disengage the friction clutch 46. Even whilethe clutch actuator control section 135 controls the clutch actuator 70so as to keep the pushing force of the friction clutch 46 at a fixedlevel, when the rotation speed of the engine 45 becomes equal to orlower than a prescribed rotation speed, the clutch actuator controlsection 135 stops controlling the clutch actuator 70 so as to keep thepushing force of the friction clutch 46 at a fixed level and controlsthe clutch actuator 70 so as to disengage the friction clutch 46. As aresult, engine stall can be prevented. The clutch actuator controlsection 135 operates in substantially the same manner while controllingthe clutch actuator 70 so as to keep the position of the friction clutch46 at a fixed position.

The shift actuator control section 140 controls the shift actuator 72.The shift actuator 72 can be driven based on the control by the shiftactuator control section 140. The shift actuator control section 140drives the shift actuator 72 based on a gear change instruction from therider. After the friction clutch 46 starts to be disengaged by theclutch actuator 70, the shift actuator control section 140 drives thetransmission mechanism 43 by use of the shift actuator 72.

The motorcycle 1 according to a preferred embodiment of the presentinvention preferably includes at least a traction control device, aclutch state detection device, a clutch actuator control device, and aclutch rotation speed difference detection device. The traction controldevice preferably includes at least the slip detection section 110 andthe engine control section 115. The clutch state detection devicepreferably includes at least the potentiometer 96 and the clutch statedetection section 105. The clutch actuator control device preferablyincludes at least the clutch actuator control section 135 and the clutchactuator 70. The clutch rotation speed difference detection devicepreferably includes at least the crankshaft rotation speed sensor 60 andthe main shaft rotation speed sensor 61.

Now, with reference to FIG. 5 and FIG. 6, control of the motorcycle 1according to the present preferred embodiment at the time of startingwill be described. FIG. 5 is a flowchart showing the control of themotorcycle 1 according to the present preferred embodiment at the timeof starting. It should be noted that the flowchart in FIG. 5 is alsoapplicable to control at the time of gear change during running. FIG. 6is a timing diagram regarding the clutch pushing force keeping controlof the motorcycle 1 according to the present preferred embodiment.Before starting (see time t0 in FIG. 6), the motorcycle 1 is at a stop,and the rotation speed of the engine 45 is an idle rotation speed. The“idle rotation speed” refers to the rotation speed of the engine 45 in aload-free state when the motorcycle 1 is at a stop. FIG. 6 is a timingdiagram of an operation performed at the time of starting of themotorcycle 1, but the control to maintain the clutch position of themotorcycle 1 according to this preferred embodiment may be performed atthe time of a gear change, namely, at the time of switching of thetransmission gear.

When the rider operates the shift switch at the time of starting of themotorcycle 1, the clutch actuator control section 135 is arranged andprogrammed to drive the clutch actuator 70 to disengage the frictionclutch 46. After the friction clutch 46 starts to be disengaged, theshift actuator control section 140 is arranged and programmed to drivethe shift actuator 72 to change the gear position of the transmissionmechanism 43 to the first gear. When the rider operates the acceleratoroperator to increase the accelerator opening at time t1 in FIG. 6, therotation speed of the engine 45 (crankshaft 25) (see reference characterc2 in FIG. 6) is increased (see an area of reference character A in FIG.6). As the rotation speed of the engine 45 increases, the clutchactuator control section 135 moves the friction clutch 46 from thedisengagement position toward the engagement position. At time t1, halfclutch control to engage the friction clutch 46 is gradually started.When the friction clutch 46 is put into the half clutch state from thedisengaged state, the torque of the engine 45 is conveyed to the mainshaft 41 via the friction clutch 46. Thus, the torque of the engine 45is conveyed to the rear wheel 23, and the motorcycle 1 starts thestarting operation.

If the half clutch state of the friction clutch 46 is continued when therotation speed of the engine 45 is low, there is an undesirablepossibility that engine stall is caused. In order to avoid this, in stepS10, the ECU 100 determines whether the rotation speed of the engine 45detected by the crankshaft rotation speed sensor 60 is lower than afirst rotation speed or not. When the rotation speed of the engine 45 islower than the first rotation speed, the control advances to step S20.By contrast, when the rotation speed of the engine 45 is equal to orhigher than the first rotation speed, the control advances to step S30.As the first rotation speed, the idle rotation speed described above,for example, can be set.

In step S20, the clutch actuator control section 135 drives the clutchactuator 70 to disengage the friction clutch 46. As a result, enginestall can be prevented. When the friction clutch 46 is disengaged instep S20, the control shown in FIG. 5 is finished. Usually, the vehicleis restarted after this.

After the half clutch control is started at time t1, the clutch rotationspeed difference (see reference character c3 in FIG. 6) is decreasedgradually. In step S30, the ECU 100 determines whether the clutchrotation speed difference of the friction clutch 46 is substantiallyzero or not (see time t2 in FIG. 6) based on the rotation speed of thecrankshaft 25 detected by the crankshaft rotation speed sensor 60 andthe rotation speed of the main shaft 41 detected by the main shaftrotation speed sensor 61 (see reference character c1 in FIG. 6). Whenthe clutch rotation speed difference is substantially zero, the controladvances to step S40 in order to finish the half clutch control. Bycontrast, when the clutch rotation speed difference is not substantiallyzero, it is regarded that the half clutch state is continued and thecontrol advances to step S70.

In step S40, since the clutch rotation speed difference is substantiallyzero, the clutch actuator control section 135 drives the clutch actuator70 to engage the friction clutch 46. Specifically, the clutch actuatorcontrol section 135 finishes the half clutch control and quickly engagesthe friction clutch 46.

In step S50, the ECU 100 determines whether a slip of the rear wheel 23is detected or not. In more detail, the ECU 100 determines whether theslip detection section 110 has detected a slip of the rear wheel 23 ornot based on the rotation speed of the rear wheel 23 detected by thedriving wheel detection sensor 92 (see reference character d1 in FIG. 6)and the rotation speed of the front wheel 12 detected by the vehiclespeed detection sensor 94 (see reference character d2 in FIG. 6). Whenthe slip detection section 110 has detected the slip of the rear wheel23, the control advances to step S60. By contrast, when the slip of therear wheel 23 is not detected by the slip detection section 110, it isregarded that the motorcycle 1 has started in a satisfactory manner andthe control on start is finished.

In step S60, since the slip detection section 110 has detected the slipof the rear wheel 23, the engine control section 115 performs thetraction control. Specifically, the engine control section 115 executesat least one of the ignition retarding control on the ignition device50, the fuel injection amount decreasing control on the fuel injectionvalve 52, and the control to decrease the opening of the throttle valve54, and thus decreases the output of the engine 45. As a result, thetorque conveyed to the rear wheel 23 is decreased, and therefore theincrease of the slip can be suppressed and prevented. When the tractioncontrol in step S60 is finished, the control shown in FIG. 5 isfinished. As a result, the slip of the rear wheel 23 is resolved, andthe motorcycle 1 finishes the starting operation.

As described above, when the determination result of step S30 is No, thefriction clutch 46 is in a half clutch state. In step S70, the ECU 100determines whether or not a slip of the rear wheel 23 is detected whilethe friction clutch 46 is in a half clutch state. In more detail, theECU 100 determines whether or not the slip detection section 110 hasdetected a slip of the rear wheel 23 based on the rotation speed of therear wheel 23 detected by the driving wheel detection sensor 92 and thevehicle speed detected by the vehicle speed detection sensor 94. Whenthe slip detection section 110 has detected the slip of the rear wheel23 (see an area of reference character B in FIG. 6), the control advanceto step S80. By contrast, when the slip of the rear wheel 23 is notdetected by the slip detection section 110, the control advances to stepS100. In the example shown in FIG. 6, the rear wheel 23 slips at timet3.

In step S80, since the slip detection section 110 has detected the slipof the rear wheel 23 (see the area of reference character B in FIG. 6),the engine control section 115 starts the traction control (see time t4in FIG. 6). Specifically, the engine control section 115 executes atleast one of the ignition retarding control on the ignition device 50,the fuel injection amount decreasing control on the fuel injection valve52, and the control to decrease the opening of the throttle valve 54,and thus starts decreasing the output of the engine 45. As a result, theoutput and the rotation speed of the engine 45 are rapidly decreased(see an area of reference character C in FIG. 6), and therefore anincrease of the amount of slip of the rear wheel 23 (difference betweenthe rotation speed of the rear wheel 23 and the rotation speed of thefront wheel 12; see reference character d3 in FIG. 6) can be suppressedand prevented.

After the processing of step S80, the control advances to step S90. Instep S90, the friction clutch 46 is in a half clutch state and the slipdetection section 110 has detected the slip of the rear wheel 23, andthus the engine control section 115 performs the traction control.Therefore, the clutch actuator control section 135 starts controllingthe clutch actuator 70 so as to keep the pushing force of the frictionclutch 46 at a fixed level (clutch pushing force keeping control) (seetime t4 in FIG. 6). As a result, the position of the friction clutch 46is kept at a fixed position and a change of the clutch position within ashort time is suppressed and prevented. Therefore, generation ofvibration based on the hunting of the clutch position can be suppressedand prevented. In addition, the rotation speed difference of thefriction clutch 46 is resolved swiftly (see the area of referencecharacter C in FIG. 6).

In step S100, the ECU 100 determines whether the clutch rotation speeddifference of the friction clutch 46 is substantially zero or not basedon the rotation speed of the crankshaft 25 detected by the crankshaftrotation speed sensor 60 and the rotation speed of the main shaft 41detected by the main shaft rotation speed sensor 61. When the clutchrotation speed difference is substantially zero, the control advances tostep S110 in order to finish the half clutch control. By contrast, whenthe clutch rotation speed difference is not substantially zero, thecontrol returns to step S70.

In step S110, since the clutch rotation speed difference issubstantially zero (see time t5 in FIG. 6), the clutch actuator controlsection 135 drives the clutch actuator 70 to engage the friction clutch46 (see an area of reference character D in FIG. 6). The pushing forceof the friction clutch 46 is kept at a fixed level, and thus theposition of the friction clutch 46 is kept at a fixed position.Therefore, the friction clutch 46 can be engaged swiftly (see time t6 inFIG. 6), and the amount of slip can be decreased swiftly. In an area ofreference character E in FIG. 6, the motorcycle 1 finishes the startingoperation. In the motorcycle 1 which has finished the startingoperation, the friction clutch 46 is in an engaged state. Therefore, thedecrease of the output and the decrease of the rotation speed of theengine 45 can be conveyed to the rear wheel 23 as they are. Thus, theslip of the rear wheel 23 is resolved. When the slip of the rear wheel23 is resolved, the engine control section 115 finishes the tractioncontrol. After the traction control is finished, the engine controlsection 115 controls the ignition device 50, the fuel injection valve52, and the opening of the throttle valve 54, and thus adjusts theoutput of the engine 45.

As described above, in the motorcycle 1 according to the presentpreferred embodiment, when the friction clutch 46 is in a half clutchstate and a slip of the rear wheel 23 is detected, the engine controlsection 115 executes the control to decrease the output of the engine45. Therefore, an increase in the amount of slip can be suppressed andprevented. In addition, when the friction clutch 46 is in a half clutchstate and a slip of the rear wheel 23 is detected, the clutch actuatorcontrol section 135 controls the clutch actuator 70 so as to keep thepushing force of the friction clutch 46 at a fixed level. As a result,even if the output and the rotation speed of the engine 45 continuedecreasing, the friction clutch 46 is kept at a fixed position.Therefore, the friction clutch 46 can be engaged swiftly. As a result,the decrease of the output of the engine 45 can be conveyed to the rearwheel 23 quickly, and thus the amount of slip of the rear wheel 23 canbe swiftly decreased. In this manner, when the friction clutch 46 is ina half clutch state and a slip of the rear wheel 23 is detected, theclutch actuator 70 is controlled so as to keep the pushing force of thefriction clutch 46 at a fixed level. Therefore, the position of thefriction clutch 46 is not changed, and vibration based on the hunting ofthe clutch position is not generated. In addition, since the frictionclutch 46 can be engaged swiftly, the amount of slip of the rear wheel23 can be swiftly decreased.

According to the present preferred embodiment, when the friction clutch46 is in a half clutch state and a slip of the rear wheel 23 isdetected, the clutch actuator control section 135 controls the clutchactuator 70 so as to keep the pushing force of the friction clutch 46 ata level thereof at the time when the slip of the rear wheel 23 isdetected. As a result, the friction clutch 46 can be engaged swiftly bythe output and the rotation speed of the engine 45 being keptdecreasing. As a result, the decrease of the output of the engine 45 canbe conveyed to the rear wheel 23 quickly, and thus the amount of slip ofthe rear wheel 23 can be swiftly decreased.

According to the present preferred embodiment, the motorcycle 1preferably further includes the cylinder main body 465 arranged to drivethe clutch actuator 70 to generate an oil pressure. When the frictionclutch 46 is in a half clutch state and a slip of the rear wheel 23 isdetected, the clutch actuator control section 135 controls the clutchactuator 70 so as to keep the oil pressure of the cylinder main body 465at a fixed level, and thus keeps the pushing force of the frictionclutch 46 at a fixed level. In this manner, the oil pressure of thecylinder main body 465 is kept at a fixed level, and thus the pushingforce of the friction clutch 46 can be kept at a fixed level.

According to the present preferred embodiment, when the friction clutch46 is in a half clutch state and a slip of the rear wheel 23 isdetected, the clutch actuator control section 135 is arranged andprogrammed to control the clutch actuator 70 so as to keep the positionof the friction clutch 46 at a fixed position. As a result, the frictionclutch 46 can be engaged swiftly by the output and the rotation speed ofthe engine 45 being kept decreasing. As a result, the decrease of theoutput of the engine 45 can be conveyed to the rear wheel 23 quickly,and thus, the amount of slip of the rear wheel 23 can be swiftlydecreased.

According to the present preferred embodiment, when the friction clutch46 is in a half clutch state and a slip of the rear wheel 23 isdetected, the clutch actuator control section 135 is arranged andprogrammed to control the clutch actuator 70 so as to keep the positionof the friction clutch 46 at a position thereof at the time when theslip is detected. As a result, the friction clutch 46 can be engagedswiftly by the output and the rotation speed of the engine 45 being keptdecreasing. As a result, the decrease of the output of the engine 45 canbe conveyed to the rear wheel 23 quickly, and thus the amount of slip ofthe rear wheel 23 can be swiftly decreased.

According to this preferred embodiment, the friction clutch 46preferably includes the friction plates 445 to which the torque of theengine 45 is conveyed and the clutch plates 449 which can be put intocontact with, and can be separated from, the friction plates 445. Inaddition, the motorcycle 1 preferably includes the crankshaft rotationspeed sensor 60 and the main shaft rotation speed sensor 61 which areused to detect the rotation speed difference between the friction plates445 and the clutch plates 449 of the friction clutch 46. When the clutchrotation speed difference between the friction plates 445 and the clutchplates 449 of the friction clutch 46 becomes substantially zero whilethe clutch actuator control section 135 controls the clutch actuator 70so as to keep the pushing force of the friction clutch 46 at a fixedlevel, the clutch actuator control section 135 stops controlling theclutch actuator 70 so as to keep the pushing force of the frictionclutch 46 at a fixed level and controls the clutch actuator 70 so as toengage the friction clutch 46. In this manner, when the rotation speedof the friction plates 445 and the rotation speed of the clutch plates449 of the friction clutch 46 become substantially equal to each other,the control to maintain the pushing force of the friction clutch 46 at afixed level is stopped and the control to engage the friction clutch 46is performed promptly. Thus, the decrease of the output of the engine 45can be conveyed to the rear wheel 23 quickly. As a result, the amount ofslip of the rear wheel 23 can be swiftly decreased.

According to the present preferred embodiment, the motorcycle 1preferably further includes the crankshaft rotation speed sensor 60arranged to detect the rotation speed of the engine 45. When therotation speed of the engine 45 becomes equal to or lower than aprescribed value while the clutch actuator control section 135 controlsthe clutch actuator 70 so as to keep the pushing force of the frictionclutch 46 at a fixed level, the clutch actuator control section 135stops controlling the clutch actuator 70 so as to keep the pushing forceof the friction clutch 46 at a fixed level and controls the clutchactuator 70 so as to disengage the friction clutch 46. In this manner,when the rotation speed of the engine 45 becomes equal to or lower thana prescribed value, the control to maintain the pushing force of thefriction clutch 46 at a fixed level is stopped and the control todisengage the friction clutch 46 is performed. Thus, engine stall can beprevented.

According to the present preferred embodiment, in the case where thefriction clutch 46 is in a half clutch state and a slip of the rearwheel 23 is not detected, the clutch actuator control section 135controls the clutch actuator 70 so as to engage the friction clutch 46when the rotation speed of the engine 45 is increased, and controls theclutch actuator 70 so as to disengage the friction clutch 46 when therotation speed of the engine 45 is decreased. As a result, the frictionclutch 46 can be engaged and disengaged easily.

According to the present preferred embodiment, the motorcycle 1preferably includes the stepped transmission mechanism 43 and the shiftactuator 72 arranged to drive the transmission mechanism 43. Since thegear position of the transmission mechanism 43 can be changed by theshift actuator 72, the operability for the rider is improved. If huntingof the clutch position occurs when the transmission mechanism 43 iscontrolled by the shift actuator 72, this may adversely influence thechange of the gear position of the transmission mechanism 43. However,in the present preferred embodiment, the hunting of the clutch positiondoes not occur. Therefore, even when the transmission mechanism 43 iscontrolled by the shift actuator 72, the change of the gear position ofthe transmission mechanism 43 is not adversely influenced.

According to the present preferred embodiment, the motorcycle 1preferably includes the shift actuator control section 140 arranged todrive the transmission mechanism 43 by use of the shift actuator 72after the friction clutch 46 starts to be disengaged by the clutchactuator 70. As a result, the change of the gear position can beperformed in a satisfactory manner.

The motorcycle 1 according to the present preferred embodimentpreferably includes the electronically controllable throttle valve 54.When a slip of the rear wheel 23 is detected, the engine control section115 can execute the control to decrease the opening of the throttlevalve 54 to decrease the output of the engine 45. In this manner, theopening of the throttle valve 54 is decreased, and thus the output ofthe engine 45 can be decreased easily.

The motorcycle 1 according to the present preferred embodimentpreferably includes the ignition device 50. When a slip of the rearwheel 23 is detected, the engine control section 115 can execute theignition retarding control on the ignition device 50 to decrease theoutput of the engine 45. In this manner, the time of igniting theignition device 50 is retarded, and thus the output of the engine 45 canbe easily decreased.

The motorcycle 1 according to the present preferred embodimentpreferably includes the fuel injection valve 52. When a slip of the rearwheel 23 is detected, the engine control section 115 is arranged toexecute the fuel injection amount decreasing control on the fuelinjection valve 52 to decrease the output of the engine 45. In thismanner, fuel injection from the fuel injection valve 52 is stopped orthe amount of fuel injection is decreased, and thus the output of theengine 45 can be easily decreased.

According to the present preferred embodiment, the motorcycle 1preferably includes the front wheel 12 rotating in accordance with therunning of the motorcycle 1, and the vehicle speed detection sensor 94includes a sensor arranged to detect the rotation speed of the frontwheel 12. As a result, the slip detection sensor 110 is arranged todetect a slip of the rear wheel 23 based on the rotation speed of thefront wheel 12 detected by the vehicle speed detection sensor 94 and therotation speed of the rear wheel 23 detected by the driving wheeldetection sensor 92.

It should be noted that the state represented by the expression “keepthe pushing force at a fixed level” as discussed above is not limited toa state where the pushing force is kept precisely at a fixed level andalso encompasses a state where the pushing force is slightly varied insuch a range that the above-described functions and effects areprovided. Also, the state represented by the expression “keep at a fixedposition” as discussed above is not limited to a state where theposition is kept precisely at a fixed position and encompasses a statewhere the position is slightly varied in such a range that theabove-described functions and effects are provided. Finally, theexpression “at the time of starting of the vehicle (motorcycle 1)” asdiscussed above refers to the time when the vehicle (motorcycle 1)starts running from the state of having a vehicle speed of zero (i.e.,the state where the vehicle is at a stop).

In the vehicle according to the present preferred embodiment, the clutchactuator control section 135 preferably is arranged and programmed tocontrol the clutch actuator 70 based on the rotation speed of the engine45. However, the clutch actuator control section 135 is not limited tothis. For example, the clutch actuator control section 135 mayalternatively be arranged and programmed to control the clutch actuator70 based on the vehicle speed detected by the vehicle speed detectionsensor 94, the opening of the throttle valve 54 detected by the throttleposition sensor 66, the accelerator opening detected by the acceleratoropening sensor, the rotation speed of the engine 45 and the like, forexample. As long as there is no change other than the change of therotation speed of the engine 45, in the case where the friction clutch46 is in a half clutch state and a slip of the rear wheel 23 is notdetected, the clutch actuator control section 135 controls the clutchactuator 70 so as to engage the friction clutch 46 when the rotationspeed of the engine 45 is increased, and controls the clutch actuator 70so as to disengage the friction clutch 46 when the rotation speed of theengine 45 is decreased. By contrast, in the case where there is a changeother than the change of the rotation speed of the engine 45 and thefriction clutch 46 is in a half clutch state and a slip of the rearwheel 23 is not detected, the clutch actuator control section 135 maycontrol the clutch actuator 70 so as to disengage the friction clutch 46when the rotation speed of the engine 45 is increased, and may controlthe clutch actuator 70 so as to engage the friction clutch 46 when therotation speed of the engine 45 is decreased.

The vehicle according to the preferred embodiments of the presentinvention is not limited to a vehicle arranged to execute semi-automaticcontrol to automatically performing the gear change based on anintention of the rider, and may alternatively be a vehicle arranged toexecute full-automatic control to automatically performing the gearchange in accordance with the driving state of the vehicle, regardlessof the intention of the rider. Instead of the clutch actuator 70 and theshift actuator 72 being provided separately, a single actuator arrangedto drive the friction clutch 46 and the transmission mechanism 43 may beprovided.

While preferred embodiments of the present invention have been describedabove, it is to be understood that variations and modifications will beapparent to those skilled in the art without departing from the scopeand spirit of the present invention. The scope of the present invention,therefore, is to be determined solely by the following claims.

What is claimed is:
 1. A vehicle comprising: an engine; a driving wheel arranged to be driven by the engine; a friction clutch located between the engine and the driving wheel; a clutch actuator arranged to disengage and engage the friction clutch; a clutch state detection device arranged to detect a half clutch state of the friction clutch; a driving wheel detection sensor arranged to detect a rotation speed of the driving wheel; a vehicle speed detection sensor arranged to detect a vehicle speed; a traction control device including a slip detection section arranged and programmed to detect a slip of the driving wheel based on the rotation speed of the driving wheel detected by the driving wheel detection sensor and the vehicle speed detected by the vehicle speed detection sensor, and an engine control section arranged and controlled to perform control to decrease an output of the engine when the slip of the driving wheel is detected by the slip detection section; and a clutch actuator control device arranged and programmed to control the clutch actuator based on a rotation speed of the engine; wherein when the friction clutch is in a half clutch state and the slip of the driving wheel is detected, the clutch actuator control device is arranged and programmed to control the clutch actuator so as to maintain a pushing force of the friction clutch at a fixed or substantially fixed level.
 2. The vehicle according to claim 1, wherein when the friction clutch is in a half clutch state and the slip of the driving wheel is detected, the clutch actuator control device is arranged and programmed to control the clutch actuator so as to maintain the pushing force of the friction clutch at a level thereof at the time when the slip is detected.
 3. The vehicle according to claim 1, further comprising a hydraulic cylinder arranged to generate an oil pressure by driving the clutch actuator, wherein when the friction clutch is in a half clutch state and the slip of the driving wheel is detected, the clutch actuator control device is arranged and programmed to control the clutch actuator so as to maintain the oil pressure of the hydraulic cylinder at a fixed level and to maintain the pushing force of the friction clutch at a fixed level.
 4. The vehicle according to claim 1, wherein when the friction clutch is in a half clutch state and the slip of the driving wheel is detected, the clutch actuator control device is arranged and programmed to control the clutch actuator so as to maintain a position of the friction clutch at a fixed position.
 5. The vehicle according to claim 1, wherein when the friction clutch is in a half clutch state and the slip of the driving wheel is detected, the clutch actuator control device is arranged and programmed to control the clutch actuator so as to maintain a position of the friction clutch at a position thereof at the time when the slip is detected.
 6. The vehicle according to claim 1, wherein: the friction clutch includes a driving-side rotation body to which a torque of the engine is conveyed and a subordinate-side rotation body arranged to be both contacted with and separated from, the driving-side rotation body; the vehicle further comprises a clutch rotation speed difference detection device arranged to detect a rotation speed difference between the driving-side rotation body and the subordinate-side rotation body of the friction clutch; and when the rotation speed difference between the driving-side rotation body and the subordinate-side rotation body of the friction clutch becomes substantially zero while the clutch actuator control device controls the clutch actuator so as to maintain the pushing force of the friction clutch at a fixed level, the clutch actuator control device is arranged and programmed to stop controlling the clutch actuator so as to maintain the pushing force of the friction clutch at a fixed level and controls the clutch actuator so as to engage the friction clutch.
 7. The vehicle according to claim 1, further comprising an engine rotation speed sensor arranged to detect the rotation speed of the engine, wherein when the rotation speed of the engine becomes equal to or lower than a prescribed value while the clutch actuator control device controls the clutch actuator so as to maintain the pushing force of the friction clutch at a fixed or substantially fixed level, the clutch actuator control device stops controlling the clutch actuator so as to maintain the pushing force of the friction clutch at a fixed or substantially fixed level and controls the clutch actuator so as to disengage the friction clutch.
 8. The vehicle according to claim 1, wherein when the friction clutch is in a half clutch state and the slip of the driving wheel is not detected, the clutch actuator control device is arranged and programmed to control the clutch actuator so as to engage the friction clutch when the rotation speed of the engine is increased and controls the clutch actuator so as to disengage the friction clutch when the rotation speed of the engine is decreased.
 9. The vehicle according to claim 1, further comprising: a stepped transmission mechanism; and a shift actuator arranged to drive the transmission mechanism.
 10. The vehicle according to claim 9, further comprising a shift actuator control device arranged to drive the transmission mechanism by use of the shift actuator after the friction clutch starts to be disengaged by the clutch actuator.
 11. The vehicle according to claim 1, further comprising an electronically controllable throttle valve, wherein, when the slip of the driving wheel is detected, the engine control section of the traction control device is arranged and programmed to execute control to decrease an opening of the throttle valve.
 12. The vehicle according to claim 1, further comprising an ignition device, wherein, when the slip of the driving wheel is detected, the engine control section of the traction control device is arranged and programmed to execute ignition retarding control on the ignition device.
 13. The vehicle according to claim 1, further comprising a fuel injection device, wherein, when the slip of the driving wheel is detected, the engine control section of the traction control device is arranged and programmed to execute fuel injection amount decreasing control on the fuel injection device.
 14. The vehicle according to claim 1, further comprising a subordinate wheel rotating in accordance with running of the vehicle, wherein the vehicle speed detection sensor is a sensor arranged to detect a rotation speed of the subordinate wheel.
 15. The vehicle according to claim 1, wherein the vehicle is a motorcycle. 